BP well declared 'effectively dead'

BP's blown-out oil well in the Gulf of Mexico has been permanently sealed, a U.S. government official said, five months after an explosion destroyed a drilling rig and led to the worst offshore oil spill in U.S. history.

Retired Coast Guard Admiral Thad Allen said Sunday that the well "is effectively dead."

Crews began pumping in cement on Friday to plug the well, about four kilometres below the sea floor.

The cement had hardened by Saturday, and a pressure test conducted has confirmed that the plug should hold.

The gusher was contained in mid-July after a temporary cap was successfully fitted atop the well. Mud and cement were later pushed down through the top of the well, allowing the cap to be removed.

But the well could not be declared dead until a relief well was drilled so that the ruptured well could be sealed from the bottom, ensuring it never causes a problem again. The relief well intersected the blown-out well Thursday, and crews started pumping in the cement the next day.

An April 20 blast killed 11 workers and over the ensuing three months allowed an estimated 780 million litres of oil to spew into the Gulf.

The disaster caused an environmental and economic nightmare for people who live, work and play along the Gulf shoreline from Florida to Texas. It also spurred civil and criminal investigations.